1. Field of the Invention
The present invention relates to a process for producing organic compounds such as lower alkyl alcohols, including ethanol, propanol (e.g. 1-propanol, iso-propanol), and butanol (e.g. 1-butanol, 2-butanol, 3-butanol, and iso-butanol) from gases including carbon dioxide, carbon monoxide, and hydrogen under thermodynamically favorable conditions; microorganisms used in the process to produce organic compounds from gases; and a process for enriching, isolating, and improving microorganisms that can be used in the process to produce organic compounds from gases. The process may also be used to produce one or more carboxylic acids including acetic acid, propionic acid, or butyric acid, other carboxylic acids, especially longer carboxylic acids, and the process produces animal feeds, and can be used to produce other products.
2. Background
Previous inventors have disclosed methods for conversion of synthesis gases (CO2, CO and H2) to lower alkyl alcohols or organic acids (For example, U.S. Pat. Nos. 5,173,429; 5,593,886; and 6,136,577, which are incorporated herein by reference). These methods use microorganisms that are fastidious and strictly anaerobic and do not tolerate high concentrations of alcohols or acids. These microorganisms have complex nutrient requirements (fastidious) or they grow very slowly or are difficult to maintain for industrial processes. For example, strictly anaerobic microorganisms do not grow, or may be killed, if exposed to even minute concentrations of oxygen. Fastidious microorganisms may require addition of growth factors that increase the cost of the process.
Aerotolerant microorganisms such as strains of Enterococcus species have been isolated and shown to also take up CO2, CO and H2, and convert these gases to lower alkyl alcohols or organic acids. For example, see the previous patent by the inventor of the present disclosure (U.S. Pat. No. 8,178,329; issued May 15, 2012), which is incorporated herein in its entirety by reference. Isolated strains of Enterococcus species produced mostly alcohols under certain conditions, and produced various acids under other conditions. They could also tolerate high concentrations of the acids and alcohols. However, even with Enterococcus species, exogenous sources of carbon such as amino acids or yeast extract were used. The inventor also disclosed isolated organisms and processes to make hydrocarbons like C2-C10 alkanes in U.S. patent application Ser. No. 13/381,127 filed on Dec. 28, 2011, which is incorporated herein in its entirety by reference. The genera of isolated microbes that made alkanes included Citrobacter and Eschericia among others, but the alkane-producing isolates had not been selected for the ability to grow on single-carbon substrates.